express-mongo simple connection

const express = require('express');

const bodyParser = require('body-parser');

const app = new express();
var DB;
var MongoClient = require('mongodb').MongoClient

MongoClient.connect('mongodb://localhost:27017/mytest', function (err, db) {
  if (err) throw err
	DB = db;	
  db.collection('crud').find().toArray(function (err, result) {
    if (err) throw err

    console.log(result)
  })
})

app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended: true}))
app.listen(4000);
console.log("port 4000");

app.get("/", function(req, res, next){
	res.json({"hi": "ashvin"});
});

app.post("/post", function(req, res, next){
	console.log(req.body);
	 DB.collection('crud').save(req.body, (err, result) => {
   		 if (err) return console.log(err)

  		  console.log('saved to database')
   		 res.redirect('/')
 	 })
	res.json(req.body);
});